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Yields and Yield Components of Flax, Soybean, Wheat, and Oats Treated with Morphactins and Other Growth Regulators for Senescence Delay¹

Objectives of this work were to determine (a) effects of regulator-promoted delay of senescence on seed yield of flax (Linum usitatissimum L.), soybean (Glycine max (L.) Merrill), wheat (Triticum aestivum (L.) em Thell), and oats (Arena sativa L.), and (b) morphological ponents of any such yield response. For flax, delay of leaf yellowing 40 to 60 days after full bloom was negatively correlated with yield for regulator applications made at vegetative, bud, and bloom stages. Postbloom applications of TIBA (9,3,5-triiodobenzoic acid) or SD-8339 (N-(phenylmethyl-9-(tetrahydro-9/-/- pyran-9-yl)-9H-purin-6-amine) delayed canopy yellowing under field conditions without affecting yield. The morphactins chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) and dichlorflurenol (methyl 2,7-dichloro-9-hydroxyfluorene-9-carboxylate) applied postbloom at rates of 95 and 100 g/ha, respectively, consistently delayed senescence of flax. Chlorflurenol significantly enhanced yield in two of six trials; dichlorflurenol increased yield in one of five trials. In spite of morphactin effects prolonging leaf and chlorophyll retention, enhancing shoot growth, and renewing flowering and fruiting, yield effectiveness was sometimes lowered by reduction in size of primary seeds, pre-harvest loss of primary fruits, and low seed set for secondary fruits. Yield enhancement by chlorflurenol was increased by application of a fungicide.

Senescence delay in soybean caused by chlorflurenol, dichlorflurenol, or BA (6-benzylamino)purine) did increase yield. Chlorflurenol treatment (500 or 1,000 g/ha) after anthesis increased seed yield of wheat, and dichlorflurenol applied in boot stage at 1,000 g/ha increased yield of oats; rate of senescence was unaltered in both crops.

Key Words: Chlorflurenol • dichlorflurenol • n-Butyl flurenol • Flurecol • 3-CPA • GA₃, GA₄,₇ • BA, BA + GA₄,₇ • Cytex • TIBA • Ethephon • Naptalam • PP528 • NC 9634 • Chlorophyll

² Research plant physiologist, USDA-SEA-ARS and associate professor, South Dakota Univ., respectively.

Received for publication December 15, 1980.